May 15 (Bloomberg) -- A trading error at Barclays Plc this
week caused split-second swings in dozens of U.S. stocks
including AOL Inc. and Caterpillar Inc., according to people
familiar with the matter.

Barclays moved the prices of some shares on May 13 after
orders tied to the close of trading were incorrectly entered,
causing the transactions to be executed immediately, the people
said. Barclays clients weren’t affected financially by the
error, and less than $4 million is probably at stake, according
to one person, who asked to not be identified because the
details haven’t been made public.

Kerrie Cohen, a spokeswoman for London-based Barclays,
declined to comment.

The mistake whipsawed companies such as AOL, Caterpillar,
Nabors Industries Ltd. and Nasdaq OMX Group Inc. According to
Winnetka, Illinois-based Nanex LLC, which tracks trading
disruptions, at least 28 stocks were affected, with AOL moving
the most: a decline of 11 percent. Within a second, prices
largely returned to where they’d been before the error.

After reviewing the situation, stock exchanges canceled
some AOL transactions. All other trades were left intact.

Knight’s Error

Erroneous equity orders and their impact on markets have
received heightened scrutiny since Knight Capital Group Inc. was
pushed to the brink of bankruptcy when a computer program went
haywire and bombarded exchanges with orders in August 2012. Last
year, U.S. Securities and Exchange Commission Chairman Mary Jo
White told U.S. market operators to review their rules for
canceling transactions.

Caterpillar, which had been trading around $107.12, jumped
to an intraday high of $108.21 within a second at 3:49 p.m. New
York time on May 13, before sinking back to where it had been.
More than $11 million worth of shares changed hands at the
elevated levels, according to data compiled by Bloomberg. AOL
sank to $32.77, a new low for the day, from around $36.85 at
about the same time as about $10 million of shares changed
hands. Prices also quickly snapped back.

Other companies with noticeable moves at the same time
include Western Union Co., Marathon Petroleum Corp., Canadian
Natural Resources Ltd., Avery Dennison Corp. and Lorillard Inc.